Electric signal pulse controlling circuits



Patented Dec. 16, 1941 E ELECTRIC SIGN t; PULSE. eoN'raor-ilme CIRCUITSof Great Britain Application March 8, 1938; Serial No. I4542 In- Gl' a/tBlitain March 1851937 3 Claims.

This invention relates to electric signal-pulse controlling -circuits=-and is of general application in circuits which inputsig nal pulsescontrol output potentials to provide,- for example, synehr'onisingpulses in television systems, automatic gain con-trolling potentials, abeat frequency-resulting'dromtwo difierent input frequencies-or signalsa multiplex signalling-sys tem.-

According to thepresen-t invention an electric signalpulse controllingormixing circuit a unidirectional conducting device or devices providetwocurrentpaths having a common pole connected-tonne end of animpedancewhichmay be'the loadimpedance-and the application of suitable controlpulses between the other end of said impedance and the other pole of oneof said unidirectional conducting devices will allow or prevent-thepassage of signals through the second unidirectional conducting device.The current paths may be constituted by the anode/cathode paths in athermionic valve or valves which may be of the diode type. The effect of.the control pulses applied between the common pole and the other poleof one of the unidirectional conducting devices may be determined bybiassing potentials applied to said common pole or said other pole or toboth said poles.

In order that the invention may be more clearly understood and readilycarried into efiect two pulse controlling circuits embodying theinvention will now be more fully described by way of example withreference to the accompanying drawing in which:

Figures 1 and 2 show such alternative forms of circuit, and

Figure 3 represents a television picture signal and synchronising pulsewaveform which may be applied to the circuit of Figure 1, for example.

Referring to Figure 1 of the drawing, a double diode valve l is providedwith one pair of input terminals 2, 3 between an anode 4 and biassingbattery 5 and another pair of input terminals 5, 1 between a resistance8 in the lead to the cathode 9 and earthed line Ill. The biassingbattery 5 is also connected to the line [0. Output terminals ll, l2 areconnected to the anode I3 and earthed line l0 respectively, and acondenser I4 and resistance l5, both shown in dotted lines, are used incertain applications of the circuit.

Assuming the circuit of Figure 1 is to be used for selecting a signalfor a specified period, this signal is applied to the input terminals 6,1.

The battery" 5 applies" to= the anodel, a positive bias potential whichis less a;negativepulse appliedto the terminals 2, 3- while thesignallis appliedto terminals- 6; 1; Until the negative pulseisappliedto the anode-' 4, the positive potential applied to this anodecauses cuirent to flow throughthe diode, the cathode ll-becomingpositive with respectto the anode 13. Thus no current can nowtothear-iode l3 and there is no output fro-m the'circuit. When the:negative pulse is applied the anode' 4' this anode ceases to takecurrentand the cathode potential falls to such a: value that theanodel-3 't'alse's current and allows the signalapplied to the'terminals 6,:1 to :passto the output terminals l-l l2;

If desired; during'th'e absence ofthe negative pulse applied toterminals2 and 3,v these terminals may be used as output terminals-for thesignalapplied to the terminals 6-,, 1-. Again',. 1the biassing potentialapplied by battery 5 to the anode 4 may be in the negative sense, thepulse applied to the terminals land 3 being positive and of greatermagnitude than the negative voltage applied by battery 5. The pulse is,of course, applied during instants at which no output from the terminals2 and 3 is required.

In an alternative application of the circuit, pulses of opposite signmay be applied to the anodes 4 and I3 respectively, and the output takenfrom anode 4 or l3. In such a case the insertion of the resistance 8 inthe cathode lead is not essential.

In the arrangement shown in Figure 2, the resistance is omitted from thecathode lead and a resistance I6 is inserted in the lead to the anodel3. The signal input is applied to terminals l1, 18 connected to theanode l3 and line Ill respectively and output terminals l9 and 20 areconnected in the cathode lead of the diode.

It is assumed that the signals to be controlled or modified are appliedbetween the terminals l1 and I8, the insertion of vthe resistance l6between the anode l3 and terminal I! not being essential. Thecontrolling signals or pulses are applied between the terminals 2 and 3and the output is taken from the cathode between the terminals 19 and20. It is further assumed that any apparatus connected between theterminals I9 and 20 will constitute a load impedance and that it is notnecessary therefore to include in the cathode lead a resistancecorresponding with the resistance 8 in Figure 1.

The anode 4 is normally biased positively so that current will flow fromthe cathode 9 to the anode 4. When the controlling or switching pulse ofnegative potential is applied to the anode 4, this anode ceases to takecurrent and the potential of the cathode falls to such an extent that acurrent flows to the anode I3 and. the signals applied to the terminalsl1, l8 provide an output at terminals 19, 20. g g

The vision signal waveform shown in Figure 3 may be used in conjunctionwith the circuit of Figure 1 to provide automatic gain controllingvoltages, the circuit including the condenser l4 and resistance l5having values of 1 microfarad and 1 megohm respectively. Thus, in orderto obtain automatic gain control itis required to produce a steadyvoltage equal to the voltage V (Fig. 3). The signal waveform with thesynchronising pulses in the positive sense is applied to the terminals6, I and a negative pulse which may be derived from the return stroke ofthe frame 'frequency blocking oscillator is applied to the terminals 2,3. During the instants that the negative pulse is applied there will bean output from the anode l3 which will be smoothed by the condenser l4and resistance I5 and will provide a gain controlling potential whichwill vary in accordance with the mean amplitude of the voltage V. V

The circuit of Figure 2 may be applied to a multiplex signalling systemof the kind described in the specification of United States Patent2,172,354 dated September, 12, 1939. Thus, U

insteadof the hexode signal, distributing valves shown in. certaincircuit arrangements described in that specification, double diodevalves operated in accordance with the presentrinvention may beemployed. In a receiver the anodes 4 of a the case of a transmitter, theoutputs are connected along a delay network and pulses appliedsimultaneously to all the anodes 4.

While a double diode valve has been described as providing the twounidirectionally conducting devices, it will be understood thatequivalent devices may be employed. Thus two separate diodes or othervalves may be employed or contact rectifier devices may be used insteadof thermionic valves. We claim: 1. An electrical signal developing meanscomprising a thermionic tube having a cathode source of electrons and atleast a first and a second electron collecting member contained withinthe envelope of said tube, means for biasing the first of said electroncollecting members to a predeterminable bias Value relatively to thecathode, a common terminal member for said electron collecting members,an input circuit connected between said cathode and said common terminalmember, impedance means connected serially with said cathode and saidcom- .mon terminal member, and an output circuit connected between saidcommon terminal and said second electron collecting member.

2. Apparatus in accordance with claim 1, wherein there is provided inaddition additional input terminal means connected between the firstelectron collecting member and the common terminal of the electroncollecting members.

3. Apparatus in accordance with claim 1,

wherein there is provided in addition a time con- WILLIAM SPENCERPERcIvAL. ERIC LAWRENCE ,CASLING WHITE.

